My craftsman mower started missing and blowing black smoke.

I have a model #917.273632 DYT4000 mower with a Briggs & Stratton 18.5hp intek plus motor with only 275 hours on it. I was mowing when it started missing and blowing black smoke. I changed the plug and it was covered with black sute, but that didn't fix it. When I try to start it, it turns over like the battery is dead (the battery is good), or it is out of time. When it does start it doesn't stay running, but while it's running I cannot hear any knocking in the motor. I think it is a valve or it is out of time, but before I start taking it apart I was wandering if there might be an electronic part I might need to check.

Black smoke and fouled plugs are usually associated with an engine that is running too rich. Check the choke plate in the carburetor and see if it is opening all the way.

Check the oil in the engine to see if it has gas in it. If the oil is mixed with gas, the seat in the inlet of the carburetor probably has some debris in it. If the float needle doesn't turn off the flow of gas from the tank, the engine will run rich and the crankcase will fill with gas. You can usually clean the debris from the inlet of the carb and the seat and replace the fuel line from the tank and solve the problem.